Final answer:
The passages given do not specify which knight encouraged Arthur to seek revenge on Lancelot, but in the Arthurian legend, Mordred is often depicted as the one who instigates conflicts.
Step-by-step explanation:
The knight who encouraged King Arthur to seek revenge on Sir Lancelot is not explicitly named in the passages provided, and without additional context, it is uncertain who this may be within the Arthurian legend. However, in many renditions of the legend, it is often Mordred, Arthur's nephew, who incites such conflicts. The passages you provided contain instances of chivalry and adventure, characteristic of Arthurian tales, but they do not directly answer the question about who advised Arthur to seek revenge on Lancelot